1. Field of the Invention
The present invention relates to an optical device well suited for application to optical communication equipment, an optical module including an optical device, and a method for mounting the optical device into the optical module.
2. Description of the Related Art
An optical device such as a micro-lens coupled with a laser diode or an optical fiber in a field of optical communication is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. Hei 07-199006 and Jpn. Pat. Appln. KOKAI Publication No. Hei 11-295561.
The former publication proposes a technology for optically coupling a laser diode and an optical fiber by using a ball lens. The latter proposes a technology for optically coupling a laser diode and an optical fiber by using an aspherical lens having a cylindrical outer periphery.
A further conventional technology is proposed for manufacturing an optical device such as a lens in the optical communication field by using photolithographic and etching processes. By this technology, for example, a desired shape such as that of a lens is formed on a silicon substrate in a photolithographic process and then unnecessary portions of the silicon are removed by etching, to form a desired optical device.
A lens proposed in the conventional technologies is arranged in a groove formed at a predetermined position in a semiconductor support substrate on which a laser diode, an optical fiber, etc. are to be installed, in such a manner that optical axes of the laser diode, the optical fiber, etc. may coincide with each other to optically couple them properly.
To couple a laser diode, an optical fiber, etc. at a high efficiency, it is necessary for a lens upon which a diffusion light emitted from the laser diode is made incident to have a lens diameter sufficiently larger than a diameter of the diffusion light. In some cases, the lens needs to have a diameter larger than that of an optical fiber to be coupled therewith.
Conventionally, however, as described in Jpn. Pat. Appln. KOKAI Publication No. Hei 11-295561, when mounting a lens, the lens is placed in a groove formed in a substrate, in such a manner that its cylindrical outer periphery may come in contact with the groove. Such a lens having a larger diameter than an optical fiber is also mounted similarly by forming such a groove that its size may be larger than an outer diameter of the optical fiber.
However, such a configuration has a drawback in improvement of mounting precision from a viewpoint of outline precision of a lens. That is, since the diameter of the optical fiber and that of the lens are different from each other, it is necessary for a groove in which the optical fiber is placed and a groove in which the lens is placed to be different from each other in cross-section or size, thereby giving a restriction that the two grooves must be formed in separate manufacturing steps. As a result, a problem occurs that a difference in the separate manufacturing steps may deteriorate the mounting precision.
To avoid this problem and improve the mounting precision, preferably a lens having the same outer diameter as that of an optical fiber to be optically coupled therewith is placed at a groove in which the optical fiber is to be mounted.
In this case, however, a maximum tolerable value of the lens outer diameter is 125 μm in the case of, for example, a typical single-mode optical fiber, so that the lens diameter is limited to this outer diameter. It has thus been difficult for the conventional technologies to improve the mounting precision without a limit in size of the lens.